Time-resolved fluorescence and solvatochromy of directly linked pyrene-DMAderivatives in alcoholic solution

Picosecond transient absorption spectroscopy and picosecond spectro-streak fluorescence measurements have been carried out in order to understand the complex photophysical dynamics of directly linked donor-acceptor systems an d the solvation dynamics in longer-chain alcohols. With these techniques, t he fast solvent response to optically generated charge transfer (CT) specie s can be followed. Studies were performed on covalently linked donor-accept or systems of the type pyrene with derivatives of N,N-dimethylaniline: dime thyl-(4-pyren-1-yl-phenyl)-amine, dimethyl-(3-methyl-4-pyren-1-yl-phenyl)-a mine and (3,5-dimethyl-4-pyren-1-yl-phenyl)-dimethylamine. The results are interpreted with particular emphasis on solvation dependent electronic rest ructuring of the CT species. We suggest a mechanism where the adiabatic ele ctronic restructuring coincides with the coupling to the torsional degrees of freedom of the solvent.